Agriculture Reference
In-Depth Information
percent hybrids. The other 50 percent will be like the lower yielding inbreds used to
form the hybrid. Making hybrid seed was at first very time consuming. Each plant
had to be hand pollinated, as in Figure 10.13. Later, it became possible to make
hybrids using special planting methods and male-sterile lines. The advantages of a
hybrid are better yields and often improved insect and disease resistance. A disadvan-
tage is that new seed must be purchased each year. This has another, less obvious,
disadvantage. There must be an existing market structure to deliver and sell the
improved seed to farmers when they need it without loss of quality or quantity. If
the seed is shipped by rail during the hot season just before rains start, there will be
loss of germination due to the heat. There will be broken bags because of improper
handling. Delays in shipment will make these losses worse. If the shipment arrives
even a few days late, farmers will plant other seed that is available and the store will
be burdened with seed it cannot sell. The use of hybrid seed requires an efficient
distribution system.
Many vegetables are hybrids. Some of the most popular tomato varieties are
hybrids requiring that new seed be purchased each planting. In addition, tomato
seeds tend to have poor viability. This means that even when treated well, only 85 to
90 percent of the seeds in the package will germinate. If the seed has been subjected
to heat, moisture, or kept over a year, the number of viable seeds will be less than
50 percent. Tomato farmers keep seeds in a cool place or a refrigerator to maintain
viability. Some seeds are very difficult to produce, and this may make them more
Figure
10.13.
Making hybrid maize.
